Skymaster Forum  

Go Back   Skymaster Forum > Messages
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Rate Thread Display Modes
  #1  
Unread 06-26-22, 08:04 PM
mshac's Avatar
mshac mshac is offline
Registered User
 
Join Date: Aug 2020
Location: North Texas
Posts: 733
mshac is on a distinguished road
Exclamation Turbocharged Manifold Pressure

My rear engine manifold pressure has been a little flaky lately. The gauge will fluctuate between say 29 and 31 inches in high-altitude cruise. I thought it was a sticky indicator gauge. It wouldn't do it all the time, but I did notice it.

The second to last flight, the rear engine would never make the same MP as the front at the same settings. It was about 2" lower. Again, I chalked it up to the gauge.

The last flight, once I got to cruise altitude of about 16K, I noticed the rear MP was at about 25" when the front was at 30". Again, it would fluctuate between about 23"-25".

My normal cruise speed was knocked down by about 15 knots, and the rear engine ran much cooler than the front at the same fuel flow settings.

The rear engine makes normal MP at lower altitudes.

So my question is this: Where do we begin troubleshooting?

The problem could be, IMHO, one of the following. Feel free to add to the list or expand on the correct testing procedures:

1. Cylinder(s) with low compression ( I'll do a leak-down test this week)
2. Intake manifold leak
3. Bad controller
4. Exhaust leak (prior to the turbo)
5. Bad turbo

Anyone with any experience chasing down this type of an issue, please chime in!!!

Last edited by mshac : 06-26-22 at 08:08 PM.
Reply With Quote
  #2  
Unread 06-27-22, 12:42 AM
wslade2 wslade2 is offline
Registered User
 
Join Date: Feb 2016
Location: none
Posts: 301
wslade2 is on a distinguished road
I’m normally aspirated so little experience with 337 turbo. But have good deal experience with ground based turbo diesels.

Looks like good list.

Exhaust leaks are under appreciated and can be hard to find with surprising effect on turbo performance. The exhaust system lives in a tough environment so very much at risk. Exhaust leaking at the cylinder of course are their own doubly problematic issue. Also, if you have intercooler don’t forget to look at that. They can shake and crack with a resultant leak.

Air filters get overlooked because they look fine but at a micro level can get obstructed.

Frequently there’s a perfect storm of a little bit of everything: declining turbo, induction leaking, exhaust leaking, dirty filter. Don’t just jump in and sentence your turbo as guilty until you look at everything.

Of course carefully check for turbo shaft play and any rubbing on the housing or oil leaking out of the turbo into induction or exhaust. Any increased oil consumption?

Last edited by wslade2 : 06-27-22 at 01:34 AM.
Reply With Quote
  #3  
Unread 06-27-22, 11:47 AM
mshac's Avatar
mshac mshac is offline
Registered User
 
Join Date: Aug 2020
Location: North Texas
Posts: 733
mshac is on a distinguished road
Thanks for the reply.

I wouldn't have thought about the filter. I'll add that to the list.

The rear engine has oil leaks like many seem to. I think it's the pushrod tube seals that are leaking, but I'll look more closely around the turbo.

Experienced input is always appreciated!
Reply With Quote
  #4  
Unread 06-27-22, 03:27 PM
ljmolina's Avatar
ljmolina ljmolina is offline
Registered User
 
Join Date: Feb 2022
Location: USA
Posts: 67
ljmolina is on a distinguished road
I am having the same issue but on my front engine. I do know when I bought the plane 2 months ago, that one of the cylinders has a low compression (55psi). I havent been able to go down the list you posted...so that give me some additional areas to check for myself.
Reply With Quote
  #5  
Unread 06-27-22, 04:22 PM
mshac's Avatar
mshac mshac is offline
Registered User
 
Join Date: Aug 2020
Location: North Texas
Posts: 733
mshac is on a distinguished road
I'll post my findings here. To anyone reading, please do the same.
Reply With Quote
  #6  
Unread 06-27-22, 08:24 PM
mshac's Avatar
mshac mshac is offline
Registered User
 
Join Date: Aug 2020
Location: North Texas
Posts: 733
mshac is on a distinguished road
The plane does have a data-recording engine monitoring system. I may spend the $100 and send the files from the last few flights to Savvy Aviation for their experts to analyze.

Anybody here ever use their service before?
Reply With Quote
Reply


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 02:10 PM.


Powered by vBulletin® Version 3.6.9
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.